In recent years, distance measurement apparatuses for measuring the distance to an object (an object to which the distance is measured) based on the parallax between a plurality of image pickup optical systems have been used for the following distance measurement for automobiles, auto focus systems for cameras, and three-dimensional shape measurement systems.
In such a distance measurement apparatus, a pair of image pickup optical systems arranged in the left-right direction or in the vertical direction form images on the respective image pickup areas, and the distance to the object is detected through triangulation using the parallax between those images.
The DFD (Depth From Defocus) method is known as a scheme for measuring the distance from a single image pickup optical system to an object. While the DFD method is an approach in which the distance is calculated by analyzing the amount of blur of the obtained image, it is not possible with a single image to determine whether it is a pattern of the object itself or a blur caused by the object distance, and therefore methods for estimating the distance from a plurality of images have been used (Patent Document 1, Non-Patent Document 1).